For example, lists of users who purchased or did not purchase a specific product or products have been obtained based on data that correlates a purchased product list to each of a plurality of users. Further, for example, lists of documents with a keyword or key words set thereon have been obtained based on data that correlates a key word list to each of a plurality of documents.
For example, the patent document 1 below describes specification of a user who did not purchase a specific product or products (e.g., a frequently purchased product or products), based on purchased product lists of a plurality of users.